In orthodontics, treatments for achieving alignment of malposed teeth in a patient include applying orthodontic appliances to the patient's teeth, such as pre-shaped orthodontic wire(s) attached to the brackets which are themselves attached to the teeth. The wires, also known as archwires, are typically made from shape memory alloys which have the ability to recover their shape after being deformed. This re-shaping occurs at a predetermined temperature, usually around 38° C. Shape memory alloys used in orthodontic archwires include nickel-titanium alloys (e.g. Nitinol™), beta-titanium alloys, and copper nickel-titanium alloys.
The wires are typically pre-shaped into a desired shape by forming bends at desired positions and with desired angles, heating under tension, and super-cooling. The heating step typically comprises electric heating. Once pre-shaped, the wire is attached to the brackets by bending its shape to conform to the general shape of the malposed teeth. When the wire warms to mouth temperature it reverts to its original shape thereby exerting a force on the teeth to which it is attached to move them.
A typical orthodontic treatment comprises a number of consecutive treatment steps in which wires of different shapes and/or stiffness may be used for applying different forces to the teeth as the alignment progresses. In some cases, the treatment steps may be classified as an aligning stage, a levelling stage, a working stage, a finishing stage and a settling stage. In some cases, the treatment stages comprise an initial stage, a transitional stage and a finishing stage. The treatment stages may include an imposed orthodontic action such as rotation or linear movement of one or more teeth, development of the arch form, a levelling of the arches, torque control or simple retention of the position. Generally, the earlier treatment stages apply more gentle forces compared to the main treatment stages. Thicker wires may be used for the more aggressive repositioning phase.
As a result, it is important for the archwire to be securely attached to the teeth of a patient during each treatment stage of the orthodontic treatment plan.